Electron multiplier voltage supply



D. R. RASLEY ELECTRON MULTIPLIER VOLTAGE SUPPLY f Filed Dec. 2, 1945 Dec. v16, 1947.

Patented Dec. 16, 1947 UNITED STATES PATENT OFFICE mesme assignments, to Farnsworth Research Corporation, a corporation of Indiana Application December 2, 1943, Serial No. 512,541

(Cl. Z50- 27) Claims.

This invention relates to signal amplifiers and particularly to voltage supplies for an electron multiplier type of amplier.

It is customary to employ multistage static electron multipliers to amplify many different types of signals. A multistage multiplier is essentially a device which is operated by impressing positive potentials of increasing values to successive ones oi the secondary emissive multiplier electrodes. In many cases it is desirable to maintain a substantially uniform potential difference between successive multiplier electrodes. One way in which this type of operation may be achieved is by use of independent sources of potentials for each pair of electrodes. Each of these sources may be chosen to impress the desired voltage upon the electrodes to which it is connected and to deliver power in the amount required by the relative magnitude of the electron current flowing between the electrodes. In this manner the source of potential between any two electrodes is not affected materially by the electron current flow between these two electrodes. Thus, the multiplication ratio of each multiplier stage and, consequently, the overall multiplication ratio of the entire device remain substantially constant throughout a considerable range of variation of the primary electron concentration at the multiplier input. The voltages developed in the output circuit of the multiplier then are substantially directly proportional to the primary electron concentrations at the multiplier input. Such a device is said to have a linear operating characteristic.

Ordinarily, however, it is more convenient to provide the electron accelerating potentials for the multiplier electrodes from taps on a voltage divider to which is connected a single source of relatively high unidirectional voltage. Where substantial linearity of response by the multiplier is required over a relatively wide range of variation in the primary electron concentrations, it is the usual practice to employ relatively low impedance components in the voltage divider. In this manner the electron current ilow in the voltage divider components constitutes but a relatively small proportion of the total current flowing in the divider. Thus, the voltage for impression upon the multiplier electrodes developed in a given voltage divider component is not affected materially by variations in the electron current ow through the component and consequently remains substantially constant.

However, the achievement of relatively good regulation of the individual voltage sources provided by such a voltage divider requires the use of a unidirectional source which is capable of delivering a substantial amount of power. One expedient which has been tried to reduce the power consumption by a voltage divider source of multiplier accelerating potentials is the use of relatively high impedance components for the divider. While the power requirements of a unidirectional voltage source are substantially reduced by such an arrangement, the performance of the multiplier is aiected in a manner which is not always desirable. In such a case the electron current flow in a given divider component constitutes a substantial proportion of the total current ow through the component. Therefore, the voltage developed at the terminals of the component is subject to an appreciable variation in accordance with the magnitude oi the electron current iiow. The overall multiplication ratio of the multiplier varies as a consequence in accordance with yariations in the magnitude of the primary electron concentrations, In such a case the operating characteristic of the multiplier no longer is linear throughout the entire operating range.

In some cases such a performance is desirable for the purpose of effecting an automatic gain control of the multiplier. within which substantial linearity of response is obtained is materially reduced with respect to the linear response ran-ge of a multiplier supplied with accelerating potentials from a relatively low impedance voltage divider.

It is an object of the present invention, therefore, to provide an accelerating voltage supply for an electron multiplier in which the power consumption is relatively low and which, at the same time, will enable the multiplier to operate in a substantially linear manner throughout a relatively wide range.

In accordance with the invention there is provided an electron multiplier having a plurality of secondary electron emissive electrodes between which there is producedV a secondary electron current ilow. The electron accelerating potentials impressed upon the multiplier electrodes are derived from a voltage divider which consists of a plurality of impedance components, one group of which is of a relatively high order of magnitude and the other group of which is of a relatively loviT order of magnitude. Individual sources of unidirectional voltages are provided for each group of the multiplier impedance components.

For a better understanding of the invention,

However, the range.

3 together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is a diagrammatic representation of a dissector tube embodiment of the invention; and

Fig. 2 is a schematic wiring diagram showing the electrical characteristics of the pertinent components of a dissector tube drawn to an enlarged scale.

Having reference now to Fig. 1 of the drawing, there is illustrated a sectional view of a dissector tube provided with an evacuated Aenvelope ii. Mounted within and adjacent to one end of the envelope is a photoelectric cathode l2. Also, within the envelope and adjacent to the end opposite the cathode, there is mounted a multistage electron multiplier housed within a .metallic shielding-anode i3. The anode is provided vwith a recessed portion it at the end of `which is formed a primary scanning Vaperture i5 which is disposed `substantially centrally with respect to the cathode i2 and faces the cathode. An accelerating anode is provided in the form of an interior wall coating iS between'the cathode 'l2 and the anode i3.

A focusing -coil il is disposed on the outside of the tube envelope Il .in a manner to surround :substantially completely the space within the tube between the cathode and the anode. A battery 'iB-or -other suitable source of electrical energy lis :connected tothe focusing coil for the energi- `zation Athereof to establish the desired focusing :field within the tube envelope -whereby an electron image is formed substantially in the plane ror .the anode i3. The tube also is provided with horizontal and vertical scanning coils I9 and 2i, respectively. Each of these coils is energized by respective sources ,22 and 23 of appropriate sawtoothedwave form voltages.

In iconjunction with 'the dissector tube there :alsozis provided an optical system represented by a lens 24, whereby an optical image of a subject "25 is focused into the plane of the photoelectric `cathode l2.

Referring now ito Fig. 2 of the drawing, a more `detailed idescription of the electrical connections .tothe yphotoelectric cathode i2 and the electron multiplier will be given. The multiplier which is housed within-the anode shield i3 comprises a plurality of box-like 'electrodes such as 25, 2l, .28 and 29. In the case of a so-called elevenstage multiplier the device includes ten of such Abox-like electrodes, the eleventh'stage ordinarily being in the Vform of a, Aplate such fas 3l. A collecting electrode of suitable form such as a grid 32is located between the tenth stage electrode 29 and the eleventh stage electrode 3l. The first stage electrode 2S is provided with -a secondary scanning aperture;33 in alignment with the primary -scanning aperture I5V formedin the anode vshield i3. The secondary aperture ordinarily is smaller than the primary aperture, being of substantially the same size as the desired elemental scanning area.

Suitable accelerating potentials are impressed -upon'the-multiplier electrodes andthe photoelectric cathode by appropriate connections to taps Von a voltage divider which, as illustrated, comprisesthe series connection of resistors 34 to 55,

inclusive. The resistors 31E-to 130 are of a relatively high order of magnitude and are connected across a source of unidirectional-voltage such as a battery 46. The requirements of this battery are that it be capable of producing a voltage of the order of 1500 volts and of delivering but relatively 'small amount of power. The resistors il to t5 are of a relatively low order of magnitude and are connected across the terminals of a source of unidirectional voltage such as a battery lll. The requirements ofthe battery il are that it be capable of `producinga voltage of the `order of 1000 volts and of delivering relatively .large amounts of power. The batteries i6 and li1 are connected in series, as shown, with the highest positive potential terminal connected to ground.

The -negative terminal of the battery d6 is connected'to the photoelectric cathode i 2. The junction point between resistors 35 and 35 Vis connected to the shielding anode I3, and also by means of an internal connection such as represented by a conductor i8k to the first stage multiplier electrode 26. Thus, the anode shield `and the first stage electrode are operated at the same positive potential with respect to the cathode l2. The electrodes comprising multiplier stages 2 to l inclusive, the latter of which is the electrode 2l, are connectedrespectively, to other` taps on the high impedance portion of the voltage divider in a manner to impress increasingly higher posi- 'tive potentials on succeeding ones of these multiplier electrodes. The eighth stage multiplier electrode 23 is connected to the junction point `between the low impedance resistances ai and 32. Similarly, the multiplier stages 9 to il are connected, respectively, to other taps on the low impedance portion of the voltage divider. For example, the tenth stage electrode Zilis'connected to the-junctionpoint between resistors .43 and-215i and the eleventh stage electrode 3l to the junctio-n point between resistors d4 and t5. The other terminal of the resistor 45 is connected Ato the grounded positive .terminalof the batteryill .and also to vone terminal of an .output resistor V139. The other terminal of the output resistor is connected to the collecting electrode32 of the vvmultiplier and also to Vone of a .pair .of .outputcircuit 'terminals 50,01 which the other terminal isconvnected to ground.

Referring now to the operation vof Athe yillustrated embodiment of the invention, it is believed that a consideration of .a concrete example .will

-serve best to demonstrate the vmanner in which sive voltage divider componentshaving values vof approximately 20,000 ohms each. The component vsimilar to resistor .Sil usually has .a value of .the

order of 30,000 ohms. The unidirectional voltage `source connected acrosssucha prior'art divider is approximately 2,500 volts, which is .the combined voltage of the present sources dit and 41, the

former being 1,500 volts and the latter 1,000 Volts.

For the present consideration the currentflow through the various voltage ,divider components resulting from the supply of electrons to the Ymultiplier electrodes willbeneglcted f0.1' theleason 'that where a low impedance divider is used, the electron currents will be'small as compared with the current circulated through Vthe .divider bythe unidirectional voltage source. Accordingly, the current ilow througha-prio-rart type of low impedance voltage dividerisapproximately -10 milliamperes, which requires that the unidirectional power source be capable of furnishing approximately 25 watts of power.

The voltage supply arrangement in accordance with this invention contemplates that the resistor 34 have a value of approximately 390,000 ohms, the resistors 35 to 40 inclusive, have values oi approximately 220,000 ohms each and resistors 4l to 45 have values of approximately 20,000 ohms each. In such a case the current supplied by the battery 46 to the high impedance portion of the divider is approximately 0.9 milliampere, thus requiring the battery to furnish approximately 1.35 watts of power. Even as in the present case where relatively high impedance, it is not inaccurate to omit consideration of the electron current flow for the reason that it is relatively small in the lower multiplier stages.

The current ow (exclusive of the electron current flow) in the low impedance portion of the divider is approximately milliamperes, requiring that the battery 41 furnish approximately 10 watts of power. It is seen that the combined power output of the batteries 46 and 41 will be approximately 11.35 watts, as compared with the 25 watt output required of a prior art unidirectional power so-urce. The power saving which results from the use of a power supply in accordance with the present invention is approximately 55%, based on the power output requirements of a prior art device of this character.

It must not be overlooked that this material saving in power consumption is realized without the loss of linearity o response by the multiplier. Extensive tests have shown that a multiplier provided with either of two power supplies, one in accordance with the prior art practice as specified hereinbefore and the other in accordance with the previously specified embodiment of the present invention, produces signal voltages in either case which correspond in a substantially linear manner to the primary electron concentrations at the multiplier input.

While there has been described what. at present, is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope oi" the invention.

What is claimed is:

1. In an electro-n multiplier, a plurality of secondary electron emissive electrodes, -a first source of unidirectional voltage, relatively high impedance means connected to said rst source of voltage for developing a first series of voltages, means for impressing said first series of voltages upon respective ones of one group of said electrodes. a second source of unidirectional voltage, relatively low impedance means connected to said second source of voltage for developing a second series of voltages, and means for impressing said second series of voltages upon respective ones of another group of said electrodes.

2. In an electron multiplier, a plurality of secondary electron emissive electrodes, a first source of unidirectional voltage having a relatively low power output capacity, relatively high impedance means connected to said first source of voltage for developing a first series of voltages, means for the voltage divider is of a A.

impressing said first series of voltages upon respective lower-numbered ones of said electrodes, a second source of unidirectional Voltage having a relatively high power output capacity, relatively low impedance means connected to said second source of voltage for developing a second series of voltages, and means for impressing said second series of voltages upon respective highernumbered ones of said electrodes.

3. In an electron multiplier, Ia plurality of secondary electron emissive electrodes, a first source of unidirectional voltage having a relatively low power output capacity, a relatively high impedance voltage divider connected across said first source of voltage, connections from individual points on said high impedance voltage divider to respective lower-numbered ones of said electrodes, a second source of unidirectional voltage having a relatively high power output capacity, a relatively low impedance voltage divider connected across said second source of voltage, and connections from individual points on said low impedance voltage divider to respective highernumbered ones of said electrodes.

4. In an electron multiplier, a plurality of secondary electronemissive electrodes, a first source of unidirectional voltage having a relatively low power output capacity, a relatively high impedance Voltage divider comprising la plurality of components of a. relatively high order of magnitude connected in series across said first source of voltage, connections from individual ones of said high impedance voltage divider components to respective lower-numbered ones of said electrodes, a second source of unidirectional voltage having a relatively high power output capacity, a relatively low impedance voltage divider comprising a plurality of components of a relatively low order of magnitude connected in series across said second source of voltage, and connections from individual ones of said low impedance voltage divider components to respective highernumbered ones of said electrodes.

5. In an electron multiplier, a plurality of secondary electron emissive electrodes, a first source of unidirectional voltage having a relatively low power output capacity, a relatively high impedance voltage divider comprising a plurality of resistors of a relatively high order of magnitude connected in series across said rst source of voltage, connections from individual ones of said high impedance voltage divider resistors to respective lower-numbered ones of said electrodes, a second source of unidirectional voltage having a relatively high power output capacity, a relatively low impedance voltage divider comprising a plurality of resistors of a relatively low order of magnitude connected in series across said second source of voltage. and connections from individual ones of said low impedance voltage divider resistors to respective higher-numbered ones of said electrodes.

DONALD R. RASLEY.

REFERENCES CITED UNITED STATES PATENTS Name Heising May Date Number 

